This invention relates to a novel, improved process of making 2,6-di-tertiarybutyl-4-mercaptophenol by a cobalt-molybdenum catalyzed reduction of bis (3,5-di-tertiarybutyl-4-hydroxyphenyl)polysulfide in the presence of hydrogen gas at a temperature range of from about 20.degree. C. to about 90.degree. C. This mercaptophenol is an intermediate in the synthesis of 4,4'-isopropylidenedithio-bis-(2,6-di-tertiarybutylphenol) which has been disclosed in U.S. Pat. No. 3,576,883 as an effective pharmaceutical agent for the reduction of serum cholesterol. This invention further relates to a novel, improved process of making 4,4'-iso-propylidenedithio-bis-(2,6-di-tertiarybutylphenyl) by further reacting the 2,6-di-tertiarybutyl-4-mercaptophenol thus formed with acetone in the presence of acid.